In general, the present invention is directed to systems and methods of treating wastewater produced by the manufacturing processes used to produce electronic components. More specifically, the present invention is directed to systems and methods for removing various components, such as but not limited to, tetra-methyl ammonium hydroxide ((CH3)4NOH, TMAH) from wastewater generated by the manufacture of opto-electronic components, such as thin-film transistor liquid crystal displays (TFT-LCDs).
As manufacturing processes in the opto-electronic and semiconductor industries advance, the composition of wastewater generated by such processes has become more complex. For example, such wastewater may comprise both organic carbon compounds and organic nitrogenous compounds, which may be poisonous, corrosive, and eutrophic to the environment.
Thin film transistor liquid crystal displays are a type of LCD that uses thin-film transistor technology to provide an active matrix LCD. TFT-LCDs are used in a variety of consumer products, such as television sets, computer monitors, mobile telphones, navigation systems, etc.
The production of TFT-LCDs in particular, generates significant amounts of high-strength organic nitrogen containing wastewater. Such wastewater may comprise various contaminants, such as TMAH—used as a developer in the production of TFT-LCDs), monoethanolamine (C2H5ONH2, MEA) and dimethyl suphoxide ((CH3)2SO, DMSO)—used as a stripper in the production, as well as chelating agents. TMAH is often used as component of the positive photoresist developers in the photolithography process of TFT-LCD manufacturing. TMAH, MEA, and DMSO are generally seen as slow biodegradable organic compounds, which during degradation typically release ammonia, resulting in a high ammonia concentration and a potential nitrification in treated wastewater.
Historically, semiconductor and electronic component manufacturing plants discharged their wastewater to local publicly owned treatment works (POTW) systems. However, the increased loading due to the recent growth of the semiconductor industries coupled with more stringent discharge regulations imposed on POTW to remove organic and nitrogen compounds from wastewater limits the ability of any such POTW to treat adequately treat such discharge.
It has been shown in the prior art that various microorganisms are capable of degrading DMSO under certain conditions. For example, Escherichi coli, Klebsiella, Serratia, Citrobacter braakii, Cyptococcus humicolus, Hyphomicrobium species, and Rhodobacter capsulatus have shown positive results in degrading DMSO. Moreover, MEA can often be degraded through a wide variety of reactions common to amine and alcohol, and can be hydrated to ammonia and acetate. Degradation of TMAH has been particularly problematic, in that the presence of TMAH has an adverse and inhibitory impact on nitrification activity.
Very little prior art addresses the application of a biological nutrient removal process for treating such wastewater, and the prior art that makes such suggestions falls unacceptably short in terms of performance. For example, in a paper entitled Nitrification-Denitrification of Opto-electronic Industrial Wastewater by Anoxic/Aerobic Process, by Chen, et at and published in the Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering, Vol. 38, Issue 10, (2003), reported a 92-98% COD removal from wastewater by using a two-stage anoxic-aerobic process, yet total nitrogen removal efficiencies were merely 70%. Moreover, as noted above, it has been recorded by several studies that the presence of TMAH inhibits biological processes. See, e.g., Use of Two-Stage Biological Process in Treating Thin Film Transistor Liquid Crystal Display Wastewater of Tetramethylammonium Hydroxide, by Han-Lin Lin, et al., and published in Sustainable Environment Research Journal, Volume 21(3), (2011); Biological Treatment of TMAH (tetra-methyl ammonium hydroxide) In a Full Scale TFT-LCD Wastewater Treatment Plant, by T H Hu, et al., and published in the Bioresource Technology Journal, (2012).
Accordingly, systems and methods for treating wastewater resulting from the production of TFT-LCDs that effectively remove TMAH as well as COD and total nitrogen are desired.